Stuff Ontology

Context

Multiple domain ontologies have various representations of types of stuff--also called matter, mass, or substance--such as milk, alcohol, and mud. This is modelled in a range of different ways that are not quite compatible with eahc other as they do not adhere to a single structured approach, at times not even within an ontology itself. While foundational ontologies and Ontology can come to the rescue to provide modelling guidance in some cases (e.g., part-whole relations), they only distinguish between pure stuff and mixtures, if it contains stuff at all.
This requires a 'bridging' core ontology to fill this gap, i.e., an ontology of categories of stuff (that is formalised in OWL for purposes of implementability). This stuff.owl core ontology aims to achieve this. It stands on its own, but there are also versions that link to the DOLCE and BFO foundational ontologies, and one with examples to illustrate classification of stuffs (among others, mayonnaise and gold). This then also resolves the main type of interoperability issues with stuffs in domain ontologies, thereby also contributing to better ontology quality.
More details, including rationale and main design decisions are described in the accompanying EKAW14 paper (see downloads). This documentation also has some modelling guidelines to facilitate the Stuff Ontology's use.

Modelling guidance example

To get a feel for what kind of things are in the stuff ontology without laoding it in your favourite ontology editor, a decision diagram is shown in the figure below.
Now consider Mayonnaise. The first question asks about the kind of thing sit is made-up of, which is more than one type of thing (mianly oil and egg yolk), so the answer is "No"; hence, Mayonnaise is a MixedStuff.
Mayonnaise's components are evenly distributed throughout, so the next answer is "Yes"; hence it is a HomogeneousMixture.
The next question requires some chemistry knowledge, so let's answer that with "Don't know", barching into the question about phases. As both oil and egg yolk are liquid before and after, they keep their phase, so, the answer is a "Yes; hence, it is a Colloid.
Because it has nothing to do with hydrophobicity or very large molecules, i.e one thing is dispersed in another, we answer with "yes"; hence, it is a Dispersion Colloid.
Considering again the phases of the constituent stuffs, both the egg yolk and oil are liquids; hence, option "a)" is chosen, and thus Mayonnaise is an Emulsion.

Interoperability principle

The point here is to outline the idea how it facilitates the interoperability, not to criticise individual domain ontologies on their modelling choices. With the stuff ontology, one categorises a stuff according to what the stuff is, irrespective of its context. For instance, Milk is a Colloid. It may have the role of Food and it may be secreted by an animal. Similarly, Blood is a Sol, while it may be part of a body. Sugar is a structured pure stuff, though one also may like to say something about its constituents (molecules), categorising those as organic compound. The Stuff Ontology, thus, helps teasing out such differences.
A similar argument holds for its relations (object properties), like granulat parts and ingredients, for which a similar argument holds, as they are now defined with unambiguous domain and range axioms.

Parts and portions

The stuff relations with respect to parthood distinguish between relating stuff universals and relating particular amounts of stuff, and between parts and portions, which extend the taxonomy of part-whole relations as depicted in the figure below. Scattered parts/portions are essentially temporal relations where the part/portion was a (contiguous) part of the whole; e.g., the wine in the wine glass that came from the bottle of wine, and the slice of the cake was part of the whole cake. Contiguous portions are still part of the whole portion, such as the top-half of the lemonade in the glass and the left-hand side of the whole cake.

Figure: Section of the basic taxonomy of part-whole relations (less and irrelevant sections in grey or suppressed), extended with the stuff relationsand their position in the hierarchy. (source: Figure 3 of the EKAW16 paper)